Electric filter device



Sept. 29, 1942. w. HAGEN 2,297,215 ELECTRIC FI'LIER DEVICE Filed May 11,1959 Fly. 1

lnvenfohm wlfqany Hqye/I Patented Sept. 29, 1942 ELECTRIC FILTER DEVICEWolfgang Hagen, Berlin, Germany; vested in the Alien Property CustodianApplication May 11, 1939, Serial No. 272,996 In Germany May 11, 1938 2Claims. (Cl. 17844) This invention relates to electric filter devices,particularly of the type adapted for use in Wireradio systems.

When telephone or other electric communication lines are employed fortransmitting intelligence or other performances by high frequencycarrier currents, a large number of electric filters is required forimpressing these high frequency currents upon such lines and forseparating the high frequency carrier currents from the low frequencyrnessage currents in the receiving positions. The type of filterscustomarily used in such wire-radio systems comprises one high-passfilter branch and one low-pass filter branch, the latter in the shape ofa coil circuit.

It has heretofore been proposed tosimultaneously employ the highfrequency coupling condensers of such filters as members of the coilcircuit of the low-pass filter branch, that is, as the shunt condensersthereof. Although this facility actually has involved a considerablestructural simplification, it has been found by tests that theattenuation characteristic obtained by lowpass filter branches of thekind in which one inductance coil is inserted in series with eachconductor of a two-wire line and in which the high frequency couplingcondensers simultaneously act as the shunt capacities of the low-passfilter branch does not involve the desired steepness, from which followsthat the filter does not present sharply defined cut-off frequencies.

My invention consists in certain features of novelty which will bereadily understood from the following description and be pointed out inthe appended claims, reference being made to the accompanying drawing inwhich Fig. 1 is a diagram explanatory of this invention, Fig. 2schematically shows an electric filter according to my invention, whileFig. 3 shows one embodiment for realizing the present invention.

It is one object of this invention to overcome the disadvantage abovementioned and to provide means in filter devices of the kind referred toabove which allow the attenuation characteristic thereof to get thedesired shape.

According to a further feature of this invention, the inductancesinserted in series with each of the conductors of a two-wire line are sotuned as to act as resonance circuits.

This effect is achieved according to still a further feature of myinvention by forming the inductance coil in two or more individuallayers of turns and to connect these layers in series with each other.This facility considerably increases the self-capacity of the inductancecoil. It is thus possible by suitably adjusting the self-capacity andthe inductance value of such coil to so adjust the resonance frequencyof the coil member that this frequency coincides with an ascendingbranch of the filter attenuation characteristic. Careful tests whichhave been carried out with a filter device designed in accordance withthe above disclosed rule gave the dash curve B of Fig. 1, in which theattenuation is plotted in the ordinate in response to the frequency asrepresented by the abscissa. The curve A, by comparison, shows theattenuation characteristic of the heretofore known filters.

An electric filter device, and more particularly the low-pass branchthereof is embodied in Fig. 2. The references a. and b denote inductancecoils, each connected in series with one conductor of a two-wirecommunication line. The high frequency message currents are appliedtothe outgoing end of a telephone subscribers line A B through atransformer D and the high frequency coupling condensers C which act asshunt capacities of the low-pass filter branch. The low frequencymessage curents to be transmitted to the subscribers line A B areimpressed upon the low-pass filter at the terminals C D. Theself-capacitance of the coils a and b is very large, and such highcapacitance value will be obtained by arranging the respective windingsin the form of two or more separate layers of turns, as shown at E and Fof Fig. 3, and by connecting each separate one of said layers in serieswith'one another. The windings of the inductances are preferablyassociated with a core of iron.

What is claimed is:

1. An electric filter device having a high-pass branch and a low-passbranch the latter in the shape of a coil circuit comprising, inductancecoils, each consisting of a plurality of windings arranged in individualparallel layers and connested in series with each other to artificiallyenhance the self-capacitance of said coils for selectively tuning themto any desired resonance frequency.

2. Electric filter arrangement comprising input and output circuits, anda low-pass filter, said filter comprising a first coil connected betweenone side of said input circuit and one side of said output circuit, asecond coil connected between the other side of said input circuit andthe other side of said output circuit, and at least one condensershunted across said output circuit, each of said coils comprising atleast two windings wound on each other and connected in series.

WOLFGANG HAGEN.

